Communication devices such as terminals are also known as e.g. User Equipments (UE), wireless devices, mobile terminals, wireless terminals and/or mobile stations. Terminals are enabled to communicate wirelessly in a cellular communications network or wireless communication system, sometimes also referred to as a cellular radio system or cellular networks. The communication may be performed e.g. between two terminals, between a terminal and a regular telephone and/or between a terminal and a server via a Radio Access Network (RAN) and possibly one or more core networks, comprised within the cellular communications network.
Terminals may further be referred to as mobile telephones, cellular telephones, laptops, or surf plates with wireless capability, just to mention some further examples. The terminals in the present context may be, for example, portable, pocket-storable, hand-held, computer-comprised, or vehicle-mounted mobile devices, enabled to communicate voice and/or data, via the RAN, with another entity, such as another terminal or a server.
The cellular communications network covers a geographical area which is divided into cell areas, wherein each cell area being served by an access node such as a base station, e.g. a Radio Base Station (RBS), which sometimes may be referred to as e.g. “eNB”, “eNodeB”, “NodeB”, “B node”, or BTS (Base Transceiver Station), depending on the technology and terminology used. The base stations may be of different classes such as e.g. macro eNodeB, home eNodeB or pico base station, based on transmission power and thereby also cell size. A cell is the geographical area where radio coverage is provided by the base station at a base station site. One base station, situated on the base station site, may serve one or several cells. Further, each base station may support one or several communication technologies. The base stations communicate over the air interface operating on radio frequencies with the terminals within range of the base stations. In the context of this disclosure, the expression Downlink (DL) is used for the transmission path from the base station to the mobile station. The expression Uplink (UL) is used for the transmission path in the opposite direction i.e. from the mobile station to the base station.
In 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE), base stations, which may be referred to as eNodeBs or even eNBs, may be directly connected to one or more core networks.
3GPP LTE radio access standard has been written in order to support high bitrates and low latency both for uplink and downlink traffic. All data transmission is in LTE controlled by the radio base station.
Spectrum efficiency is an important factor when operators are trying to keep up with the steady traffic growth in Global System for Mobile communications (GSM) systems today. Spectrum refarming, which refers to when some parts of the frequency spectrum that was assigned to GSM are assigned to other radio access technologies, such as, e.g., LTE and High Speed Packet Access (HSPA), puts an even higher demand on spectrum efficiency for the GSM network in order to continue to serve existing traffic. Also, the available transmission power in a radio unit may today be regarded as a common resource to the services the radio unit serves. For example, a radio unit that has a maximum output power of 50 Watts (N) and serves both GSM and LTE, may restrict the output power to a maximum of 20 W for GSM, and 30 W for LTE. Thus, the 20 W for GSM may need to be used efficiently, and the possibility of decreasing the overall output power may be useful. Decreasing the output power may also lower interference, both within GSM, but also between GSM and LTE-carriers that may be using the GMS frequency spectrum.
Measurement Report-Based Power Control
Power control algorithms that may be used for Circuit Switched (CS) services today are most commonly based on radio measurements that are reported by a radio node to the node or nodes serving it. For example, the radio measurements may be reported to a Base Station Controller (BSC) as Received signal QUALity (RXQUAL) and received signal strength or Received signal LEVel (RXLEV), measured on active bursts during a time period, such as a Slow Associated Control Channel (SACCH) period, SUB of FULL measurement set. Because the SACCH period may last 480 ms, the radio signal quality reporting period is relatively long, as it may typically occur every SACCH period of 480 ms interval. One or more of these measurements are reported to the BSC, or an equivalent node, as a so called Measurement Report (MR). An MR may comprise one measurement of signal quality and/or strength of a radio channel between the node sending the MR, and the node receiving the MR. For example, the MR may comprise RXQUAL or RXLEV measurements. In some particular embodiments, the MR may correspond to the measurement report described in 3GPP TS 45.008, version 12.3.0. The MR may be used as input to the power control algorithm in the BSC or equivalent node, which may calculate an appropriate output power for the BTS the BSC controls, DL, and the mobile station served by such BTS, UL.
FIG. 1 shows an example of the performance of a MR-based power control, in terms of how many speech frames may be sent and with what power. In this case it is a BTS providing the output power down-regulation in deciBels (dB). The bar chart shows the results of the power control in a live network recording from an area of around 600 cells. In total, about 73 000 frames were recorded. The Figure shows the percentage of speech frames sent for each amount of down regulation, with one bar for each power range. The data represented in FIG. 1 corresponds to live recorded data from a large area. As the Figure shows, there are a high fraction of speech frames that are sent with full power in a live network, that is, with 0 down regulation. If the speech frames sent with full output power are excluded, that is, if the bar for the 0 down regulation is excluded, the target down regulation is around 6 dB, i.e. when the connections reach a stable power value. That is, the average power for a speech frame may be approximately 6 dB below the full power. In this example, some connections are down regulated further since they probably have very good radio signal conditions.
A connection subjected to a channel change may most probably start from full power once it is established on the new radio resource. This may also contribute to the high number of speech frames sent with full power.
FIG. 1 shows that, in a live network, although after a stable connection, the average power down regulation of the recorded 73000 frames, excluding the frames with 0 down regulation, is approximately 6 dB, a high fraction of frames are still sent with full power. Thus, MR-based power control algorithm is not very efficient as the fraction of frames that are still sent on full power is high.
Adaptive Multi Rate (AMR) Codec Mode Adaptation
Another one of the existing power control systems is the AMR codec mode adaptation power control algorithm, also referred to herein as the AMR power control algorithm, described e.g., in WO2005/034381 A1. A codec is an apparatus to code audio data, or another type of data. The codec may be used to compress the data, but also to add redundancy such that it may be possible to decode the data after some parts of the coded data have been lost, e.g. when it is transmitted over the air through a radio channel. There may be in this case restrictions on the throughput and latency for the coded data, e.g. how much data may be transmitted per time unit. If no data is expected to be lost in the transmission, a codec with little or even no redundancy may be used. This may allow transmitting the audio with the highest quality. If a lot of data is expected to be lost in the transmission, a robust codec with a lot of redundancy may need to be used. This may represent lower audio quality. It may be possible to reduce the number of lost data by increasing the output power. It may also be possible to correct faulty decoded data, that has been identified as faulty decoded, by retransmitting the corresponding data. This may reduce the throughput of the data and most probably also reduce the audio quality. It may also be allowed to discard faulty decoded or lost data. This may reduce the audio quality.
Thus, based on the quality of the channel, audio quality requirements and power consumption requirements, a codec and a transmission power may be selected.
The AMR codec mode defines a source codec bit rate and the channel rate, i.e. full rate or half rate channel. Codecs are grouped into sets where it may be easy to change codec within the set, e.g. since part of the processing is common, but difficult to change to a codec in another set. An active codec mode set may be defined as the set the currently used codec belongs to. A codec mode position is the position within the active codec set. An active codec set may consist of up to 4 different codec modes, all using the same channel rate. The first position in the active codec set may represent the codec mode with the lowest bit rate, e.g., CODEC_MODE_1 in 3GPP TS 45.009, version 12.0.0. If the active codec set includes more than one codec mode, the second position may refer to the second lowest bit rate, e.g., CODEC_MODE_2 in 3GPP TS 45.009, version 12.0.0. If the active codec set includes more than two codec modes, the third position may refer to the third lowest bit rate, e.g., CODEC_MODE_3 in 3GPP TS 45.009, version 12.0.0, and if the active codec set includes four codec modes, the fourth position may refer to the highest bit rate, e.g., CODEC_MODE_4 in 3GPP TS 45.009, version 12.0.0.
AMR may use an inband signalling procedure that allows for the codec mode to adaptively change every second speech frame within an Active Codec Set, i.e. on a 40 ms basis, according to 3GPP TS 45.009, version 12.0.0. Thus, every 40 ms, a node such as a mobile station may send a codec mode request to another node, such as the BTS, telling which codec rate to use within the active codec set. The request may be based on the estimated Carrier to Interference level (C/I) related to the thresholds sent to the mobile station at call setup, or channel change. An UL Mode Request may give an indication of the quality perceived at the mobile station. An UL Mode Request is a request that may be sent by radio node, e.g., a mobile station, indicating which codec it desires the DL data to be coded with, in order to obtain certain audio quality, e.g., a better audio quality than a current audio quality. A request for a lower codec mode may indicate that the C/I is low and a more robust codec may be used to obtain acceptable speech quality. A request for a higher codec mode may indicate that the C/I has improved. Thus, better speech quality may be obtained with a codec using a higher data rate.
Power Control Based on Mode Request Signaling
Existing solutions have proposed to utilize the AMR codec mode signaling just described in a DL, and potentially also in an UL, as a power control algorithm that potentially may operate with a faster feedback time than 480 ms. This faster feedback may allow for more aggressive regulation procedure towards acceptable speech quality targets. However, a power control algorithm based on the AMR codec mode signaling may be too unstable.
Given the foregoing, the existing methods for power regulation provide inadequate support to the increasing demands for spectrum efficiency.